There has been known a method of manufacturing a semiconductor device where a glass layer for passivation is formed such that the glass layer covers a pn junction exposure portion in the process of manufacturing a mesa-type semiconductor device (see patent literature 1, for example).
FIG. 14A to FIG. 14D and FIG. 15A to FIG. 15D are views for explaining such a conventional method of manufacturing a semiconductor device. FIG. 14A to FIG. 14D and FIG. 15A to FIG. 15D are views showing respective steps of the conventional method.
The conventional method of manufacturing a semiconductor device includes, as shown in FIG. 14A to FIG. 14D and FIG. 15A to FIG. 15D, “semiconductor base body forming step”, “trench forming step”, “glass layer forming step”, “photoresist forming step”, “oxide film removing step”, “roughened surface region forming step”, “electrode forming step”, and “semiconductor base body cutting step” in this order. Hereinafter, the conventional method of manufacturing a semiconductor device is explained in the order of these steps.
(a) Semiconductor Base Body Forming Step
Firstly, a p+ type diffusion layer 912 is formed by diffusion of a p type impurity from one surface of an n− type semiconductor substrate (n− type silicon substrate) 910, and an n+ type diffusion layer 914 is formed by diffusion of an n type impurity from the other surface of the n− type semiconductor substrate 910 thus forming a semiconductor base body in which a pn junction arranged parallel to a main surface of the semiconductor base body is formed. Thereafter, oxide films 916, 918 are formed by thermal oxidation on a surface of the p+ diffusion layer 912 and a surface of the n+ type diffusion layer 914 respectively (see FIG. 14A).
(b) Trench Forming Step
Next, predetermined opening portions are formed on the oxide film 916 at predetermined positions by photo etching. After etching the oxide film, subsequently, the semiconductor base body is etched thus forming trenches 920 having a depth exceeding the pn junction from one surface of the semiconductor base body (see FIG. 14B).
(c) Glass Layer Forming Step
Next, a layer made of the glass composition for protecting a semiconductor junction is formed on inner surfaces of the trenches 920 and a surface of the semiconductor base body in the vicinity of the trenches 920 by an electrophoresis method, and the layer made of the glass composition for protecting a semiconductor junction is baked so that a glass layer 924 for passivation is formed on surfaces of the trenches 920 (see FIG. 14C).
(d) Photoresist Forming Step
Next, a photoresist 926 is formed such that the photoresist 926 covers a surface of the glass layer 924 (see FIG. 14D).
(e) Oxide Film Removing Step
Next, the oxide film 916 is etched using the photoresist 926 as a mask so that the oxide films 916, 918 in a portion 930 where an Ni plating electrode film is formed are removed (see FIG. 15A).
(f) Roughened Surface Region Forming Step
Next, surface roughening treatment is applied to a surface of the semiconductor base body in the portion 930 where the Ni plating electrode film is formed thus forming a roughened surface region 932 for increasing adhesion between the Ni plating electrode and the semiconductor base body (see FIG. 15B).
(g) Electrode Forming Step
Next, an Ni plating is applied to the semiconductor base body thus forming an anode electrode 934 on the roughened surface region 932, and forming a cathode electrode 936 on the other surface of the semiconductor base body (see FIG. 15C).
(h) Semiconductor Base Body Cutting Step
Next, the semiconductor base body is cut by dicing or the like at a center portion of the glass layer 924 thus dividing the semiconductor base body into a plurality of chips whereby mesa-type semiconductor devices (pn diodes) 900 are formed (see FIG. 15D).
As has been explained heretofore, the conventional method of manufacturing a semiconductor device includes the step of forming the trenches 920 exceeding the pn junction from one surface of the semiconductor base body where the pn junction arranged parallel to the main surface is formed (see FIG. 14A and FIG. 14B), and the step of forming the glass layer 924 for passivation in the inside of the trench 920 such that the glass layer 924 covers a pn junction exposure portion (see FIG. 14C). Accordingly, in the conventional method of manufacturing a semiconductor device, by cutting the semiconductor base body after forming the glass layer 924 for passivation in the inside of the trench 920, mesa-type semiconductor devices having high breakdown strength can be manufactured.